High frequency beam tube having an r.f. shielded and insulated collector

ABSTRACT

A high frequency velocity modulated beam tube is disclosed having a beam collector structure insulated from the body of the tube. A high frequency conductive housing surrounds the insulator structure to prevent stray radiation from the tube. A wave energy attenuator is disposed in the housing to minimize excitation of high Q resonant modes in the housing. The attenuator comprises plural turns of a dielectric conduit having a cooling liquid flowing therethrough. In a preferred embodiment the conduit forms the attenuator which is cooled by the liquid. In another embodiment the coolant is lossy to form the attenuator.

United States Patent 91 Levin July 24, 1973 [54] HIGH FREQUENCY BEAM TUBE HAVING AN R.F. SHIELDED AND INSULATED COLLECTOR [75] Inventor: Martin E. Levin, Burlingame, Calif.

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: June 16, 1969 [21] Appl. No.: 833,516

12/1960 Schneider et al 313/31 X 6/1968 Amaud 313/36 X [57] ABSTRACT A high frequency velocity modulated beam tube is disclosed having a beam collector structure insulated from the body of the tube. A high frequency conductive housing surrounds the insulator structure to prevent stray radiation from the tube. A wave energy attenuator is disposed in the housing to minimize excitation of high Q resonant modes in the housing. The attenuator comprises plural turns of a dielectric conduit having a cooling liquid flowing therethrough. In a preferred embodiment the conduit formsthe attenuator which is cooled by the liquid. in another embodiment the coolant is lossy to form the attenuator.

6 Claims, 3 Drawing Figures PATENTEUJULZMSB INVENTOR. MARTIN E. LEVIN Y a 2 ATTOR EY HIGH FREQUENCY BEAM TUBE HAVING AN R.F. SHIELDED AND INSULATED COLLECTOR DESCRIPTION OF THE PRIOR ART Heretofore, .high frequency velocity modulation tubes have employed beam collectors insulated from the body of the tube with a conductive housing surrounding the insulator to prevent stray radiation from the tube. However, it was found that high Q resonant modes of oscillation were sustained within the housing which resulted in producing arcing across the insulator.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved high frequency velocity modulation tube of the type employing a beam collector insulated from the body of the tube.

One feature of the present invention is the provision of a high frequency energy attenuator in a radiation shielding housing surrounding an insulator which insulates the beam collector structure from the body of the tube, whereby excitation of high Q modes of oscillation within the housing is minimized in use.

Another feature of the present invention is the same as the preceding feature wherein the attenuator includes a length of dielectric conduit having a liquid coolant flowing therethrough to carry away the heat generated in the attenuator.

Another feature of the present invention is the same as the immediately preceding feature wherein the dielectric conduit is made of a lossy dielectric material for attenuating wave energy within the housing.

Another feature is the same as the second feature wherein the liquid coolant is lossy for attenuating wave energy within the housing.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal view, partly in section and partly schematic, of an electron tube employing features of the present invention,

FIG. 2 is an enlarged sectional view of a portion of the structure of FIG. 1 delineated by line 2-2, and

FIG. 3 is a schematic circuit diagram depicting a current interception monitoring circuit as employed with the tube of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a high frequency velocity modulated beam tube 1, such as a 40 to 200 KW beam input power UHF klystron amplifier, incorporating features of the present invention. The tube 1 includes an evacuated envelope having an electron gun assembly 2 at one end for forming and projecting a beam of electrons 3 over an elongated beam path to a beam collector structure 4 disposed at the terminal end of the beam path and at the other end of the envelope. A high frequency interaction circuit 5, such as a succession of cavity resonators 6, is arranged along the beam path 3 intermediate the gun 2 and the collector 4. The interaction circuit 5 forms the main body portion of the tube 1 and interacts with the beam to produce velocity and current density modulation of the beam in a manner well known in the art. A pair of mag netic pole pieces 7 and 8 are provided at opposite ends of the interaction circuit for mating with a solenoid, not shown, to produce an axially directed magnetic field therebetween within the beam path 3 for focusing the beam 3 through the interaction circuit 5. Output high frequency energy is extracted from the interaction circuit 5 via an output coupling means, such as coupling loop 9 at the terminal end of the circuit 5. An output transmission line, such as a coaxial line 11, is coupled to the loop 9 for transmitting the output power to a suitable utilization device, such as an antenna, not shown.

The beam collector structure 4 (see FIGS. 1 and 2) includes a hollow cylindrical beam collecting bucket 12, as of copper, having a plurality of longitudinally directed cooling fins 13 formed in the outside surface thereof. The beam collector bucket 12 includes a constricted entrance port 14 aligned with the beam 3 and an outwardly directed circular flange portion 15. A tubular jacket 16, as of 0.063 inch thick stainless steel tubing, coaxially surrounds the collector bucket 12 and is sealed in a watertight manner, as by solder, to the marginal lip of the flange portion 15, at 17. The annular region 18 between the collector bucket 12 and the surrounding jacket 16 defines the boiler of a vaporization cooler and is filled with a liquid coolant, such as purified and deionized water. The energy of the collected beam 3 is converted into heat which is transferred to the coolant by boiling the coolant in the boiler region 18. The boiling coolant rises and passes out the open end of the jacket 16 through a conduit, not shown, to a condenser, not shown, and is returned to the base of the boiler 18 via inlet pipe 19. Typical flow rates are 0.07 gallons per minute for each 10 KW of power dissipated by the collector 12.

The collector 4 is supported in spaced relation from the collector pole piece 8 via a plurality of insulative blocks 21, as of alumina ceramic disposed about the periphery of the flange portion 15 of the collector bucket 12. An insulative vacuum tight joint is formed between the collector bucket 12 and the pole piece 8 via an insulative ring 22, as of alumina ceramic, brazed to annular Kovar frame members 23 and 24. Frame member 24 is brazed to the collector pole piece 8, whereas frame member 23 is welded to a second frame member 25 which in turn is brazed to outer periphery of collector flange 15.

An annular sheet metal housing member 26 surrounds the insulator 22 to minimize unwanted radiation of high frequency energy from the tube 1. More particularly, the current density modulation on the beam induces high frequency energy into the annular gap 27 between the collector flange 15 and the collector pole piece 8. This energy would normally propagate radially through the gap 27 and through the insulator 22 to the surrounds if it were not for the housing member 26. The housing member 26 is conductively connected to the collector pole piece 8 via a mounting ring 28, as of brass, via screws 29. The mounting ring 28 is in turn conductively connected to the pole piece 8 via screws 31. The other end of the housing member is connected to the collector jacket 16 via a cylindrical bypass capacitor structure 32.

The bypass capacitor structure 32 includes an outer cylindrical capacitive plate 33 formed by a cylindrical sheet metal member, as of 0.030 inch thick brass, coaxially disposed of the collector jacket 16. A double thickness of nylon sheet insulation as of 0.005 inch to 0.010 inch thick is wrapped around the collector jacket 16 and sandwiched between the outer plate 33 of the bypass capacitor and the inner plate of the capacitor formed by jacket 16. The housing member 26 is joined conductively to capacitor plate 33 at 34, as by a solder joint. The housing member 26 defines with capacitor 32, jacket 16 and pole piece 8 a chamber 35 having a portion surrounding the insulator 22.

A high frequency attenuator structure 36 is disposed in the annular chamber 35 to attenuate wave energy therein and to minimize excitation of high frequency high Q modes of oscillation therein which otherwise build up excessive r.f. fields across the insulator 22 causing arcing and fracture of the insulator 22 or unwanted radiation. The attenuator 36 comprises a plurality of turns of dielectric conduit 37 wrapped around the collector within the annular air filled chamber 35. One end of the conduit 37 is connected in liquid communication with the input pipe 19, whereas the other end of the conduit is connected to a pipe fitting 38 which passes through the collector jacket 16 into the boiler region 18, such that the liquid coolant for the collector flows through the conduit 37 for removing heat generated in the attenuator structure 36.

In a preferred embodiment, the dielectric conduit 37 is made of a lossy dielectric material, such as fiveeighths inch to three-fourths inch neoprene rubber hose, which is lossy for high frequency energy (UHF) and insulative for relatively low frequencies and d. c. In this embodiment, the flow of liquid coolant, which need not be lossy, removes the heat generated in the lossy conduit 37. In another embodiment, the dielectric conduit 37 need not be lossy and the liquid coolant flowing through the conduit 37 is made lossy for absorbing the high frequency energy and carrying away the heat. Suitable lossy coolant liquids include a dilute aqueous solution of Sodium Dichromate.

Referring now to FIG. 3 there is shown the electrical circuit to permit monitoring beam current interception on the interaction circuit and beam current collected by the collector 4. A known impedance 41 is connected between the cathode of the gun 2 and the negative terminal of the collector-to-cathode power supply 42. A voltmeter 43 is connectd across the impedance 41 for measuring the voltage drop thereacross and, thus, to obtain a measure of total beam current. A tap 44 of the power supply is grounded and the tap is connected to the interaction circuit 5 for grounding same. A second known impedance 45 is connected in series between the collector end of the power supply 42 and the collector 4. A voltmeter 46 is connected across impedance 45 to measure the voltage drop thereacross caused by the collector current and, thus, to obtain a measure of the collector current. Subtraction of the monitored collector current from the total beam current yields the current intercepted by the body. This measurement is typically employed to adjust the field of the beam focusing solenoid to obtain minimum body current.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a high frequency beam tube having an evacuated envelope, means for forming and projecting a beam of electrons over an elongated beam path, means at the terminal end of the beam path for collecting and dissipating the energy of the beam, means disposed along the beam path for electromagnetic interaction with the beam to produce current density modulation thereof, means for electrically insulating said beam collector means from said interaction means to permit monitoring of body current collected by said interaction means and said beam collecting means, said insulator means forming a gas tight portion of the evacuated envelope of the beam tube, means forming a bypass ca pacitor structure connected in parallel with said insulator means for bypassing high frequency current around said insulator means, a conductive housing at least partially defining with said bypass capacitor and said collector means a chamber having a portion surrounding said insulator means, THE IMPROVEMENT COM- PRISING, wave energy absorbing means electrically insulative at relatively low frequencies and wave absorptive at the relatively high operating frequency of the tube, said absorbing means disposed in said chamber for absorbing wave energy therein.

2. The apparatus of claim 1 wherein said wave energy absorbing means comprises a dielectric conduit connected for passing a liquid coolant therethrough.

3. The apparatus of claim 2 wherein said dielectric conduit is relatively lossy at high frequencies and wherein said liquid coolant serves to carry away heat generated by absorption of wave energy in the walls of said lossy conduit.

4. The apparatus of claim 2 wherein said energy absorbing means includes the liquid coolant which is relatively lossy at high frequencies for absorbing and carrying away the heat generated by absorption of the wave energy in said lossy liquid.

5. The apparatus of claim 2 wherein said conduit is coiled in a plurality of turns around said collector means within said chamber.

6. The apparatus of claim 2 wherein said conduit is made of rubber. 

1. In a high frequency beam tube having an evacuated envelope, means for forming and projecting a beam of electrons over an elongated beam path, means at the terminal end of the beam path for collecting and dissipating the energy of the beam, means disposed along the beam path for electromagnetic interaction with the beam to produce current density modulation thereof, means for electrically insulating said beam collector means from said interaction means to permit monitoring of body current collected by said interaction means and said beam collecting means, said insulatOr means forming a gas tight portion of the evacuated envelope of the beam tube, means forming a bypass capacitor structure connected in parallel with said insulator means for bypassing high frequency current around said insulator means, a conductive housing at least partially defining with said bypass capacitor and said collector means a chamber having a portion surrounding said insulator means, THE IMPROVEMENT COMPRISING, wave energy absorbing means electrically insulative at relatively low frequencies and wave absorptive at the relatively high operating frequency of the tube, said absorbing means disposed in said chamber for absorbing wave energy therein.
 2. The apparatus of claim 1 wherein said wave energy absorbing means comprises a dielectric conduit connected for passing a liquid coolant therethrough.
 3. The apparatus of claim 2 wherein said dielectric conduit is relatively lossy at high frequencies and wherein said liquid coolant serves to carry away heat generated by absorption of wave energy in the walls of said lossy conduit.
 4. The apparatus of claim 2 wherein said energy absorbing means includes the liquid coolant which is relatively lossy at high frequencies for absorbing and carrying away the heat generated by absorption of the wave energy in said lossy liquid.
 5. The apparatus of claim 2 wherein said conduit is coiled in a plurality of turns around said collector means within said chamber.
 6. The apparatus of claim 2 wherein said conduit is made of rubber. 